The present invention relates to the production of polyethylene glycol (PEG) modified polyester compositions that are suitable for forming fibers. The present invention also relates to the making of yarns and fabrics from these copolyester fibers.
Polyester filament is strong, yet lightweight, and has excellent elastic memory characteristics. Polyester fabric resists wrinkles and creases, retains its shape in garments, resists abrasions, dries quickly, and requires minimal care. Because it is synthetic, however, polyester is often considered to have an unacceptable appearance for garment purposes when the polyester is initially formed as a filament. Accordingly, polyester filaments require texturing to produce acceptable yarn and fabric characteristics with respect to appearance, hand, and comfort. Even then, polyester garments are often viewed unfavorably by consumers.
In pursuit of improved polyesters, various chemical modifications have been attempted to obtain desirable textile features. Unfortunately, some such treatments can produce unexpected or unwanted characteristics in the modified polyester. For example, polyethylene glycol enhances certain polyester properties, such as dye uptake, but diminishes other properties, especially those melt phase characteristics that are critical to filament spinning. Consequently, manufacturers have found that significant fractions of polyethylene glycol in copolyester can complicate-and even preclude-the commercial production of acceptable copolyester filaments. To gain commercial acceptance, modified polyesters must be compatible with commercial equipment with respect to melt-spinning, texturing, yarn spinning, fabric forming (e.g., weaving and knitting), and fabric finishing. This need for processing compatibility through conventional equipment has constrained the development of innovative polyester compositions.
To overcome the limitations of polyester compositions, polyester fibers are often blended with other kinds of fibers, both synthetic and natural. Perhaps most widely used in clothing are blended yarns and fabrics made of polyester and cotton. In general, blended fabrics of polyester and cotton are formed by spinning blended yarn from cotton fibers and polyester staple fibers. The blended yarns can then be woven or knitted into fabrics.
Cotton, like polyester, has certain advantages and disadvantages. Cotton is formed almost entirely of pure cellulose. Cotton fibers are typically about one inch long, but can vary from about one-half inch to more than two inches. Mature cotton fibers are characterized by their convolutions. Under a microscope, cotton appears as a twisted ribbon with thickened edges. Cotton is lightweight, absorbs moisture quickly and easily, and has a generally favorable texture (i.e., hand) when formed into fabrics. Cotton, however, lacks strength characteristics and elastic memory. Consequently, garments formed entirely of cotton require frequent laundering and pressing.
Blends of cotton and polyester fibers have found wide-ranging acceptance as they combine the desirable characteristics of each. Even so, there are continuing efforts to develop polyester filament, yarns, and fabrics that more closely resemble those of cotton, silk, rayon, or other natural fibers. One example is polyester microfibers, which are characterized by extremely fine filaments that offer exceptionally good aesthetics and hand, while retaining the benefits of polyester. Polyester microfibers, however, have proved to be difficult to dye because of their high degree of molecular orientation and crystallinity.
Accordingly, a need continues to exist for enhanced polyester compositions that have certain properties similar to those of cotton and other natural fibers, while retaining the advantages of polyester. One such composition and method for producing the same is disclosed by Nichols and Humelsine in commonly-assigned, pending U.S. patent application Ser. No. 09/141,665, filed Aug. 28, 1998, for Polyester Modified with Polyethylene Glycol and Pentaerythritol, now U.S. Pat. No. 6,294,254. U.S. patent application Ser. No. 09/141,665, which is incorporated entirely herein by reference, discloses a polyester composition that includes polyethylene terephthalate, polyethylene glycol, and chain branching agent in quantities sufficient to prepare a polyester composition that permits filament manufacture under substantially normal spinning conditions with a resulting filament that possesses physical characteristics superior to those of unmodified polyester filaments. As known to those familiar with the manufacture of filament, the equipment used to spin polyester filament is designed, built and adjusted to handle polymers whose melt viscosity falls within a certain range, typically between 500 and 4000 poise.
Another method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending U.S. patent application Ser. No. 09/444,192, filed Nov. 19, 1999, for a Method of Preparing Polyethylene Glycol Modified Polyester Filaments, now U.S. Pat. No. 6,454,982. U.S. patent application Ser. No. 09/444,192, which, as noted, is incorporated entirely herein by reference, describes copolymerizing polyethylene glycol, which typically makes up between about 4 percent and 20 percent by weight of the resulting copolyester, into polyethylene terephthalate in the melt-phase to a relatively low intrinsic viscosity (i.e., a viscosity that will not support filameent spinning). The resulting PEG-modified polyester is then further polymerized in the solid phase until the copolyester is capable of achieving a melt viscosity sufficient to spin filaments. By introducing a solid state polymerization (SSP) step, this method reduces the need to add branching agents, such as pentaerythritol, to increase the melt-phase polymerization rate and thereby achieve an intrinsic viscosity that facilitates the spinning of filaments.
A related method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending application Ser. No. 09/484,822, filed Jan. 18, 2000, for Polyethylene Glycol Modified Polyester Fibers and Method for Making the-Same, now U.S. Pat. No. 6,291,066. U.S. patent application Ser. No. 09/484,822, which is a continuation-in-part of the aforementioned application Ser. No. 09/444,192 and, as noted, is also incorporated entirely herein by reference, describes copolymerizing polyethylene glycol and branching agent into polyethylene terephthalate in the melt-phase to form a copolyester composition having an intrinsic viscosity of at least about 0.67 dl/g. Thereafter, copolyester filaments can be spun from the copolyester composition.
A related method for making nonwoven fabrics formed from such enhanced polyester fibers is described by Carnes and Branum in commonly-assigned, pending application Ser. No. 09/761,446, filed Jan. 17, 2001, for Nonwoven Fabrics Formed From Polyethylene Glycol Modified Polyester Fibers And Method For Making The Same. U.S. patent application Ser. No. 09/761,446, which is a continuation-in-part of the aforementioned application Ser. No. 09/484,822 and, as noted, is also incorporated entirely herein by reference, describes copolymerizing polyethylene glycol and branching agent into polyethylene terephthalate in the melt-phase or, alternatively in the solid-phase, to form a copolyester composition, which is then formed into copolyester fibers. Thereafter, copolyester fibers are formed into nonwoven fabrics.
With the exception of Ser. No. 09/141,665, these commonly-assigned applications relate to copolyester compositions having relatively low amounts of branching agent (e.g., below about 500 ppm pentaerythritol). In contrast, U.S. application Ser. No. 09/141,665 relates to copolyester compositions including branching agents in an amount sufficient to raise the melt viscosity of the composition to a level that permits filament manufacture under conditions that are substantially the same as those under which filament can be formed from unmodified polyethylene terephthalate.
Conventional wisdom suggests that high levels of branching agents can lead to excessive cross-linking, which in turn leads to relatively weaker filaments and textiles. There are instances, however, where weaker filaments are desirable. For example, pilling of polyester-containing fabrics has long been viewed as undesirable. As will be known by those familiar with fabrics, pills are small, twisted spheres of fiber that remain firmly attached to the fabric. Without being bound to a particular theory, it is thought that pilling in cotton/polyester blends occurs when the weaker cotton fibers break during wear, thereby loosening the fabric. The stronger polyester fibers then work their way out of the fabric to form pills at the fabric surface. It is believed that pilling can be reduced by using weaker polyester fibers. Unfortunately, weaker fibers also tend to break during filament spinning, thereby causing process disruptions.
Therefore, it is an object of this invention to provide
PEG-modified copolyester fibers possessing favorable characteristics similar to those possessed by natural fibers while retaining the advantages of polyester, and that can be formed into exceptionally comfortable woven, knit, and nonwoven fabrics.
Another object of the present invention is to provide a PEG-modified copolyester fiber that possesses superior wicking, drying, and dyeing characteristics as compared to commercially-available polyester fibers.
Yet another object of the present invention is to provide a PEG-modified copolyester composition that includes an amount of branching agent sufficient to provide viscosity properties suitable for spinning in commercial spinning equipment.
Yet another object of the present invention is to provide a method of copolymerizing polyethylene glycol into polyethylene terephthalate (PET) to achieve a PEG-modified copolyester composition that is readily spun into filaments.
As will be understood by those of ordinary skill in the art, modifying conventional polyesters with polyethylene glycol can improve certain polyester characteristics, yet can adversely affect others. For example, adding polyethylene glycol to polyethylene terephthalate improves wicking, but slows melt-phase polymerization kinetics. It also depresses melt viscosity and renders the processing of such PEG-modified copolyesters somewhat impractical in commercial polyester spinning operations.
Accordingly, in one aspect the invention is a modified copolyester composition that is suitable for use in commercial polyester spinning operations. This composition is particularly well-suited for forming fibers that can be formed into exceptionally comfortable fabrics. The fibers include polyethylene terephthalate in an amount sufficient for the copolyester fibers to possess dimensional stability properties substantially similar to those of conventional, unmodified polyethylene terephthalate fibers. The fibers also include polyethylene glycol in an amount sufficient for the copolyester fibers to possess wicking properties that are superior to those of conventional, unmodified polyethylene terephthalate fibers. Typically, the polyethylene glycol has an average molecular weight of less than about 5000 g/mol. The fibers also include a chain branching agent in an amount between than about 0.0014 and 0.0113 mole-equivalent branches per mole of standardized polymer, the standardized polymer being unmodified polyethylene terephthalate. Preferably, the copolyester fibers have a zero-shear melt viscosity of between about 1000 and 3500 poise when heated to 260xc2x0 C.
In another aspect, the invention is a PEG-modified copolyester fiber formed of particular polymer chains. As before, this fiber can be formed into exceptionally comfortable fabrics that include polyethylene terephthalate in an amount sufficient for the copolyester fiber to possess dimensional stability properties substantially similar to those of conventional, unmodified polyethylene terephthalate fibers. The modified copolyester fiber also includes polyethylene glycol in an amount sufficient for the copolyester fiber to possess wicking properties that are superior to those of conventional, unmodified polyethylene terephthalate fibers. Preferably, polyethylene glycol has an average molecular weight of less than about 5000 g/mol. This modified copolyester fiber also includes a chain branching agent in an amount between about 0.0014 and 0.0113 mole equivalent branches per mole of standardized polymer, the standardized polymer being unmodified polyethylene terephthalate.
Preferably, this copolyester fiber primarily includes polymer chains formed from structural units consisting essentially of diol monomers, aromatic non-substituted diacid monomers, and branching agent monomers. The copolyester fiber has a zero-shear melt viscosity of between about 1000 and 3500 poise when heated to 260xc2x0 C.
In another aspect, the invention is a nonwoven fabric formed of PEG-modified copolyester fibers, such as staple fibers or continuous filaments, that provide exceptional moisture management characteristics. As discussed previously, the copolyester fibers of this embodiment include polyethylene terephthalate, polyethylene glycol, and chain branching agent.
In another aspect the invention includes a PEG-modified copolyester composition that is particularly suitable for fibers. The composition includes polyethylene terephthalate in an amount sufficient for a fiber made from the composition to possess dimensional stability properties substantially similar to those of conventional unmodified polyethylene terephthalate fibers. The composition also includes polyethylene glycol in an amount sufficient for a fiber made from the composition to possess wicking properties that are superior to those of conventional, unmodified polyethylene terephthalate fibers, wherein the polyethylene glycol has an average molecular weight of less than about 5000 g/mol.
The copolyester composition also includes a chain branching agent that will copolymerize with polyethylene terephthalate, such as trifunctional alcohols, trifunctional acids, tetrafunctional alcohols, pentafunctional alcohols, pentafunctional acids, hexafunctional alcohols, or hexafunctional acids. The branching agent is present in the copolyester composition in an amount between about 0.0014 and 0.0113 mole equivalent branches per mole of standardized polymer, the standardized polymer being unmodified polyethylene terephthalate.
The composition preferably includes polymer chains formed from structural units consisting essentially of diol monomers, aromatic non-substituted diacid monomers, and branching agent monomers. Furthermore, the composition preferably achieves a zero-shear melt viscosity of between about 1000 and 3500 poise when heated to 260xc2x0 C.
In yet another aspect, the invention is a method of preparing PEG-modified copolyester fibers that can be formed into exceptionally comfortable fabrics. The method includes copolymerizing polyethylene glycol and a chain branching agent into polyethylene terephthalate in the melt phase to form a copolyester composition having a zero-shear melt viscosity of between about 1000 and 3500 poise when heated to 260xc2x0 C. The polyethylene terephthalate is present in the copolyester composition in an amount sufficient for fiber made from the copolyester composition to possess dimensional stability properties substantially similar to those of conventional, unmodified polyethylene terephthalate fibers. The polyethylene glycol has an average molecular weight of less than about 5000 g/mol and is present in an amount sufficient for a fiber made from the copolyester composition to possess wicking properties that are superior to those of conventional, unmodified polyethylene terephthalate fibers. The chain branching agent is present in the copolyester composition in an amount between about 0.0014 and 0.0113 mole equivalent branches per mole of standardized polymer, the standardized polymer being unmodified polyethylene terephthalate. Thereafter, the copolyester composition is spun into filaments.
In yet another aspect, the invention is a method of preparing PEG-modified copolyester fibers that can be formed with spandex fibers into exceptionally comfortable fabrics. The method includes copolymerizing polyethylene glycol and a chain branching agent into polyethylene terephthalate in the melt phase to form a copolyester composition that achieves a zero-shear melt viscosity of between about 1000 and 3500 poise when heated to 260xc2x0 C. The polyethylene terephthalate is present in the copolymer composition in an amount sufficient for a fiber made from the copolyester composition to possess dimensional stability properties substantially similar to those of conventional, unmodified polyethylene terephthalate fibers. The polyethylene glycol has average molecular weight of less than about 5000 g/mol and is present in an amount sufficient for a fiber made from the copolyester composition to possess wicking properties that are superior to those of conventional, unmodified polyethylene terephthalate fibers. The chain branching agent is present in the copolyester composition in an amount between about 0.0014 and 0.0113 mole equivalent branches per mole of standardized polymer, the standardized polymer being unmodified polyethylene terephthalate.
Thereafter, the method according to this embodiment includes forming copolyester fibers from the copolyester composition, blending the copolyester fibers with spandex fibers, and dyeing the blended copolyester fibers and the spandex fibers at a temperature of about 260xc2x0 F. or less.